RE: RMAN impact

As everyone else said, Rman does have an impact on the database. But
how are you backing up your database now?
The benefit of using Rman is the ease of performing backups an
especially the ease of recovering from a loss. And, the database is up
all the time rather than taking a cold backup.

I just started to look into RMAN backup and recovery and have a
question: for example, it takes 2 hours for RMAN to backup the database,
how much impact will RMAN have on the database during this 2 hours? Will
user be able to access the database during this 2 hours?